zebra: Allow blackhole singleton nexthops to be v6

A blackhole nexthop, according to the linux kernel,
can be v4 or v6.  A v4 blackhole nexthop cannot be
used on a v6 route, but a v6 blackhole nexthop can
be used with a v4 route.  Convert all blackhole
singleton nexthops to v6 and just use that.
Possibly reducing the number of active nexthops by 1.

Signed-off-by: Donald Sharp <[email protected]>

Author: donaldsharp

zebra/zebra_nhg.c

@@ -356,18 +356,23 @@ void zebra_nhe_init(struct nhg_hash_entry *nhe, afi_t afi,
 	 */
 	if (nh && (nh->next == NULL)) {
 		switch (nh->type) {
-		case NEXTHOP_TYPE_IFINDEX:
-		case NEXTHOP_TYPE_BLACKHOLE:
 			/*
 			 * This switch case handles setting the afi different
-			 * for ipv4/v6 routes. Ifindex/blackhole nexthop
+			 * for ipv4/v6 routes. Ifindex nexthop
 			 * objects cannot be ambiguous, they must be Address
-			 * Family specific. If we get here, we will either use
-			 * the AF of the route, or the one we got passed from
-			 * here from the kernel.
+			 * Family specific as that the kernel relies on these
+			 * for some reason.  blackholes can be v6 because the
+			 * v4 kernel infrastructure allows the usage of v6
+			 * blackholes in this case.   if we get here, we will
+			 * either use the AF of the route, or the one we got
+			 * passed from here from the kernel.
 			 */
+		case NEXTHOP_TYPE_IFINDEX:
 			nhe->afi = afi;
 			break;
+		case NEXTHOP_TYPE_BLACKHOLE:
+			nhe->afi = AFI_IP6;
+			break;
 		case NEXTHOP_TYPE_IPV4_IFINDEX:
 		case NEXTHOP_TYPE_IPV4:
 			nhe->afi = AFI_IP;